Science fiction has rocked cinemas for a century, and the genre has produced many undisputed classics during that time. But which movies are essential viewing for anyone interested in the genre? We broke down the 25 must-watch science fiction films.

Methodology: We looked at a few different criteria, including overall cinematic excellence. We wanted to include films that were important to the development of the genre, and which had helped to raise the overall level of awesomeness in science fiction films. We also wanted to represent as many different types of films as possible. And we looked for films that had an original concept, or which were the first of their kind in some way.

But most of all, we looked for films that would represent science fiction well to a new audience and totally rock a neophyte's brain.

Obviously, a list like this can never be 100 percent definitive, and we may have left your favorite movie of all time out — feel free to disagree and post your own lists in comments!

Metropolis (1927, dir. Fritz Lang) This film is one of the most formative works of science fiction of all time, and its imagery remains potent nearly 80 years later. And now that there's a fully restored version finally hitting cinemas — for the first time ever, outside of Germany — you can finally appreciate Fritz Lang's vision in its entirety. With its uniquely weird storyline involving a worker's uprising and a woman's robot duplicate, Metropolis remains a source of fascination — but it's also the source of much of the work that comes after it.

The Day The Earth Stood Still (1951, dir. Robert Wise) The 1950s were the era of sensational movies about aliens and monsters threatening our way of life — but only The Day The Earth Stood Still dares to use that framework to make us question that way of life. Klaatu's visit to us, and the warning he delivers, still resonate today. With its thought-provoking premise, this film won praise from such luminaries as Arthur C. Clarke, who put it on his own list of the best science fiction films.

Forbidden Planet (1956, dir. Fred M. Wilcox) A formative classic of space opera, this is said to be the first movie to take place on another planet, in deep space. It's often described as a retelling of Shakespeare's The Tempest, but Forbidden Planet also manages to do something unique, with a monster that comes from within and its secret relationship to the mysterious scourge that wiped out the super-advanced Krell race, 200,000 years ago. Like TDTES, this film examines our own tendency towards self-destruction, but it delves into the psychology of human self-destructiveness more.

Planet Of The Apes (1968, dir. Franklin J. Schaffner) And then there's this version of humanity's encounter with the "other" — Charleton Heston is the indignant everyman, thrust into a world where humans are little better than beasts and apes are ascendant. With their stinking paws. This film launched a whole genre of films in which a lone human (sometimes Heston again) copes with an inhuman who have inherited our planet and transformed it in their own image. But this film is still arguably the best.

2001: A Space Odyssey (1968, dir. Stanley Kubrick) A total departure from everything that came before, this film benefited immensely from Kubrick's unique eye as well as Arthur C. Clarke's mixture of hard science fiction and interest in transcendance. It's almost hard to list everything this film did first, and better than anybody else since: A compelling, realistic description of life in space? A depiction of an artificial intelligence going mad? A huge mystery that spans from the dawn of humanity into our far future? Those are just the building blocks for a film that's as mind-blowing and rewarding of close attention today as it was in 1968. It's also given us some of the genre's most quotable dialogue.

Alien (1979, dir. Ridley Scott) This film didn't just launch Scott and star Sigourney Weaver — it also launched a whole genre of movies about our terrifying encounters with creatures beyond our own imagination. Scott merged space opera, Westerns and horror in a way that pretty much nobody had done before, and the result remains vivid today. With a sharp script by Dan O'Bannon and note-perfect direction by Scott, this is a master class on how to do creepiness and a compelling story in the sterility of deep space.

Star Wars: The Empire Strikes Back (1980, dir. Irvin Kerschner). This is the first of three sequels that came out in the early 1980s that were better than the films they followed, but which also innovated in a way that their precursors didn't. Not that the original Star Wars wasn't innovative — it was, in many ways, including its breathtaking effects, its fresh take on Western and Samurai themes, and its exhilerating approach to space opera. But Empire Strikes Back took all of the formal brilliance of Star Wars and married it to a story that feels truly epic. Luke Skywalker's journey in the film, from near-death on Hoth to confronting his own darkness on Dagobah to learning the truth on Bespin — this is a real voyage of discovery. You couldn't skip any of those steps and have it still work. All our other heroes struggle with tragedy and adversity — especially Han Solo — and it makes them deeper and more magnetic as characters. This isn't just the best Star Wars movie, it's one of the most essential movies, in any genre.

Mad Max 2: The Road Warrior (1981, dir. George Miller) And then there's this — the first Mad Max film is brutal and awesome, and well worth watching again, especially if you've only seen the dubbed version. But where Mad Max shows the breakdown of Max and the civilization he lives in, this sequel shows the aftermath, and becomes an indelible classic of post-apocalyptic films in the process. The final huge convoy scene, with its demolition derby feeling, has influenced everything that came after. And with "peak oil" once again being a hot topic, this film's story of barbarians struggling over the last oil supplies has a new resonance.

Star Trek II: The Wrath Of Khan (1982, dir. Nicholas Meyer) Like Empire Strikes Back, this film rises above its status as just another installment in a big, commercial saga. You could show this movie to someone who had never seen any Trek, and it would still resonate on a hundred different levels. James Kirk is the ultimate neophile, who always wants to go forward and rediscover new worlds, but he's been doing it too long and now his past is chasing him everywhere he goes. He's got a son and an arch-enemy that he didn't know he had, and the twist — that the ultimate weapon is also a source of renewal that can literally create life where none existed before — sets up one of the most bittersweet endings in movie history. And then there are the space battles, which are totally different than Star Wars and yet indelibly awesome in their own right.

Blade Runner (1982, dir. Ridley Scott) I think Scott's the only director who gets represented twice on this list, and with good reason — Blade Runner is just as essential as Alien, in its own way. It's still just as visually unique now as it was when it came out, and it defined the look and feel of cyberpunk as well as urban dystopia. And you can't even talk about science fiction noir without delving into Blade Runner. And like many of the other films on this list, Blade Runner looks at what it means to be human by examining our interactions with the "other" — but the line gets so blurry, and the Replicants so fascinating, that the end result is something you have to chew over in the hours after watching.

E.T. (1982, dir. Steven Spielberg) A lot of people may hate on this film, but it changed the way we see first contact with aliens, and E.T. was one of the first really compelling aliens ever to appear on the big screen. E.T. takes the sense of wonder from Close Encounters Of The Third Kind and makes it more intimate and personal. This is also the movie in which Spielberg's obessions with fatherhood, children and discovery resonate the best. But also, from a technical standpoint, it's an amazing achievement — rewatch it sometime, and look at how everything is presented from a child's eye-level, and the mom is the only adult whose face we see in the first two acts. Spielberg uses lighting, camera angles and dialog to make a film that's not just about childhood, but told from a child's point of view.

Tron (1982, dir. Steven Lisberger) It's hard to understate how much this film changed the genre of science fiction — it's arguably the first movie to use computer generated effects, as Lisberger hung out at MIT and learned from the techies there — but it's also still one of the most thrilling depictions of virtual worlds on the big screen. (Compare Tron to Lawnmower Man to see how much more exciting and believable the earlier film is.) With the theme of fighting against the fascistic Master Control Program, Lisberger manages to update science fiction's longstanding interest in social change, but makes it fun and exciting rather than dreary and preachy.

Back To The Future (1985, dir. Robert Zemeckis) It's shocking how few truly great science fiction comedy films there are — I wanted to include Galaxy Quest on this list really badly — but BTTF would still tower above the rest even if there were tons. It's clever and yet never stops being about Marty McFly and his family. It manages to come up with a coherent theory of time travel, in which you can rewrite the past and the effects are seen nearly instantaneously (luckily, Marty is only missing like an arm and a leg before the timestream rights itself) and never becomes inconsistent. And it's surprisingly daring, jumping feet first into the tricky waters of time-traveling incest. Plus it's one of those science fiction movies that everybody, even genre-hating snobs, will admit to loving.

Brazil (1985, dir. Terry Gilliam) And 1985's other classic film is also a comedy... well, sort of. It's possibly the darkest, bleakest, most horrifying comedy you'll ever see, with freakish plastic surgery, a man being condemned to death because of a typographical error, a lecture on ducting and a vigilante plumber. This is my favorite movie of all time, and probably the best thing to come out of Monty Python after the television series. This film probably couldn't get made today, and it definitely wouldn't get made in Hollywood, which tried to neuter it in U.S. cinemas. A subversive masterpiece, this film changed what a lot of people thought was possible in dark comedy as well as dystopian film-making.

RoboCop (1987, dir. Paul Verhoeven) Another totally subversive science fiction movie from the 1980s, this film picks up Tron's obsessions with corporate fascism and runs in a different direction, with the evil OCP trying to take over Detroit's police force and remake the struggling city as Delta City. RoboCop himself is a great example of science fiction's struggle with the ways technology changes or negates our humanity, and 20 years before The Dark Knight, this film manages to delve into similar questions about how far we'll go to keep society safe from crime. A surreal blend of cyberpunk, Frankenstein and action movie, this film remains Verhoeven's greatest statement.

Terminator 2: Judgment Day (1991, dir. James Cameron) Speaking of dark action movies that confront us with questions about what it means to be human — this film would deserve a spot on the list just for the scene in which John Connor opens up the Terminator's head and changes his brain from read-only to read/write, so the Terminator can begin to learn from his experiences instead of just following commands. But it's also a brilliant action movie, in which every action sequence is inventive and uses special effects in a clever way. Every big-budget, CG-heavy action film aspires to be Terminator 2 deep in its chrome heart.

Ghost In The Shell (1995, dir. Mamoru Oshii) Like Akira, this is one of the first anime films to hit the U.S. and make a big impact, and impress on U.S. fans how powerful anime film-making was becoming. It's spawned a huge franchise, which for the most part hasn't diluted the awesomeness of the concept at all — Stand Alone Complex is considered one of the greatest science fiction anime shows, and it wouldn't exist without this film. With its theme of possibly false memories and cyber-weirdness, it had a huge influence on both cyberpunks and memory-altering works like Dark City and Dollhouse, but it turns into an amazing examination of the theme of sentience and the definition of life.

The Matrix (1999, dir. the Wachowskis) Forget the colossal letdown of the sequels — viewed as a standalone film, this is a brilliant action movie that spawned a million imitators, but it also put an end to an entire sub-genre. There were a slew of dark cyberpunk movies in the late 1990s that mixed weirdness and clever intrigue, with a sense that nothing was real — and The Matrix basically ended that subgenre by being so good, the others paled by comparison. (Have you even heard of Cyberwars? The 13th Floor?) And this film asked philosophical questions about the nature of reality, while feeding us our messianic candy in a way that didn't leave us sick to our stomachs afterwards.

Primer (2004, dir. Shane Carruth) Weirdly, this film and Back To The Future stand together as the two great time travel movies, and they couldn't be more different. Primer is famous as a film that you need to watch a few times before you fully grasp what's going on, and there's never been a movie that was less eager to explain itself to its audience. The opening, in which a couple of nerds tinkering in their garage randomly hit on an amazing discovery, is one of the great iconic nerd scenes of all time, and then the movie just gets crazier and crazier, with our heroes going back in time a few times too often until they descend into a kind of insanity. Worth watching just for the Walkman scene. This film is what Lost was trying to do with its own time travel stories.

The Incredibles (2004, dir. Brad Bird) It took immense self-control not to load this list up with a ton of films from the Pixar guys, including Wall-E and The Iron Giant. (Yes, I know Giant wasn't a Pixar film, but it's directed by Brad Bird.) But The Incredibles is arguably the best Pixar film, and the best superhero film, of all. This film takes the mythos of the Fantastic Four and mashes it up with a bit of Watchmen, and the result manages to be just as fun as the former and almost as dark and thought-provoking as the latter. And The Incredibles does something no other superhero film — including, I'd argue, Marvel's recent self-made efforts — has pulled off: it feels like a fully realized superhero universe, in which there are superhero costume makers, and tons of larger-than-life challenges all the time, including big robots and supervillains. We can only hope a live-action superhero film will rise to this movie's challenge some day.

Eternal Sunshine Of The Spotless Mind (2004, dir. Michel Gondry). This film works on so many levels. It's a metaphor for the ways in which you try to erase someone from your memories and your life, after a breakup, in order to reinvent yourself as a single person. And yet, the film manages to suggest, that process is a form of suicide — you have to destroy a piece of your life in order to excise your former lover from it. And since that process is also the reverse of falling in love, maybe it leads you to realize why you fell for the other person in the first place. But Eternal Sunshine is also an incredibly clever science fiction movie that introduces a bizarre new technology in a way that's both surreal and believable.

Children Of Men (2006, dir. Alfonso Cuarón) On the surface, this film is about a dystopian future in which humans can no longer procreate, and society falls into madness. But it quickly turns into a metaphor for immigration and xenophobia, as the United Kingdom tries to shut out the rest of the world. No film has depicted sheer chaos as kinetically and memorably as this one has, especially in its epic final single-take action sequence. Unpredictable, dazzling and well-made, Children Of Men sets the standard for gritty science fiction action movies.

Moon (2009, dir. Duncan Jones) Yes, we're putting three movies from the last couple years on this list, and there are a few other recent films that were strong candidates as well, including Wall-E, Avatar and The Dark Knight. As much as it's true that we're drowning in a sea of derivative garbage, as Hollywood tries to churn out as many cookie-cutter films and sequels as possible, some really original and clever films have sneaked through. Moon is both a throwback to old-school film-making (mostly practical effects, a single massive set that was built in its entirety and sealed up during filming) and a huge step forward in terms of using special effects in a clever, inobtrusive way. (The central trick, of having two Sam Rockwells, could not have been done without CG effects, and the DVD gives some insight into just how hard it was to pull off.) This movie manages to make the theme of corporate evil and the nature of selfhood, that pops up in so many films on this list, and make it totally fresh by throwing in a horrifying twist, in which Rockwell's character turns out to be disposable in the most literal sense. Well worth watching a second time, even if you saw it in theaters.

District 9 (2009, dir. Neill Blomkamp). The other great indie film of 2009, this quasi-documentary feels like an old-school Doctor Who story about a human turning into something unrecognizeable, wrapped around a totally savage message film. There's seldom been a less sympathetic protagonist than Wikus, who's a pusillanimous cog in a brutal machine — the scene where he casually slaughters alien children and jokes about the popping sound still makes me ill — but we wind up identifying with him and his plight as he's cast out of society anyway. That makes a more powerful statement than if Wikus were a noble champion of the downtrodden from the beginning. And while Wikus finally sort of redeems himself, it's shocking how late it comes. Plus, this is another great action movie that actually uses action sequences in an inventive way. Despite its crude stereotypes of Nigerians, this remains an important, influential film.

Inception (2010, dir. Christopher Nolan). It's already clear that this film that will stand as one of the genre's most important works — like Eternal Sunshine, it examines the nature of consciousness in a clever way that still makes sense in the end. And like Wrath Of Khan, it's about a man who's being swallowed up by his past, except that in this case Dom Cobb is actually haunted by a literal ghost, and he's in constant danger of being pulled so deep into a kind of netherworld that he'll never escape. But as a clever caper that revolves around a brilliantly inventive new technology and keeps reinventing itself every few minutes, Inception does what only the truly great science fiction films pull off: it makes science fiction a nexus of different genres, in which every genre is enriched by its contact with the speculative.

Additional reporting by Mary Ratliff. Thanks also to Alasdair Wilkins and Meredith Woerner.